Create a new document in Photoshop. Add a new layer and using your Shape tool(Rounded Rectangle Tool) create a shape like this... The edges are set at 16 px to create the rounded sides.

Add a new layer and create a rectangle in the same color and overlap the bottom of the shape above.

Next click on the first layer and then shift-click the second shape layer. Both layers should be highlighted blue. Now right-click and select Merge Layers. Now you've got a nice button shape.

Now you need to apply the bubble look by using a Layer Style. Double click on the button layer in your layers window. The layer style box will pop-up. Click on Bevel and Emboss. I adjusted the depth, size and soften until I got the bubble look I preferred.

Now create a text layer and add your text. Double click on the layer in the layers window again and apply the Stroke style. I used 50% opacity and a 1 px stroke. I then used the same Stroke style on the button to give the button a nice finished look.